This invention relates to abrasive bodies.
Cubic boron nitride (CBN) compacts are well known in the art and consist of a polycrystalline mass of CBN particles bonded into a hard conglomerate. The CBN content of compacts is at least 70 percent by volume and generally between 80 to 90 percent by volume.
CBN compacts may be self-bonded without the aid of a bonding matrix or second phase. Alternatively, such compacts may be produced where there is a suitable bonding matrix or second phase. When a second phase or bonding matrix is present, it will generally contain a catalyst (also known as a solvent or sintering aid material) for cubic boron nitride growth. Examples of suitable catalysts are aluminium or an alloy of aluminium, nickel, cobalt, iron, manganese or chromium.
The presence of a catalyst for CBN is desirable because then under the conditions necessary for the manufacture of a CBN compact some intergrowth between the particles is likely to occur. As is known in the art, CBN compacts are manufactured under conditions of temperature and pressure at which the abrasive particle is crystallographically stable.
CBN compacts can be used in a variety of abrading applications such as cutting, grinding, drilling, turning and the like. For such applications, they may be bonded to a suitable tool or shank. Alternatively, they may be bonded to a cemented carbide backing or support which is then bonded to the tool or shank.
CBN compacts bonded to a cemented carbide support, called composite compacts, have been described in the patent literature and are in commercial use. The CBN compact may be bonded directly to the cemented carbide support without the interposition of a bonding layer. Such composite compacts and their manufacture are described, for example, in U.S. Pat. Nos. 3,743,489 and 3,767,371. Bonding of CBN compacts to cemented carbide supports may also be through a metal or alloy bonding layer. Such are described in U.S. Pat. No. 4,063,909. The bonding layers described in this specification include high temperature braze metals such as titanium, tantalum, nickel, cobalt, iron, chromium, manganese, vanadium, molybdenum, or platinum and alloys containing one or more of these metals, either alone or with a low temperature braze.
Bonding of CBN compacts to cemented carbide supports using commercially available silver and copper based alloys have not proved successful because cracks and laminations have been found to occur at the compact/alloy interface in use.